A power supply device which becomes a driving source of an electric motor of a hybrid vehicle, an electric vehicle, and the like is formed by forming a set of battery cell assembly by assembling in parallel a plurality of unit cells from which positive electrodes and negative electrodes are protruded from the top faces thereof and connecting positive electrodes and negative electrodes of adjacent unit cells with each other in series, and further connecting a plurality sets of this battery cell assembly.
In such a power supply device, a positive electrode and a negative electrode of each unit cell that constitutes the battery cell assembly are connected to electrodes of adjacent unit cells in series by a conductor such as a busbar. Also, in the power supply device, electric wires for voltage detection are utilized for successively detecting and monitoring a voltage of each unit cell that constitutes the battery cell assembly, and terminals for connection between these electric wires and the positive electrodes and negative electrodes are provided on the battery cell assembly.
As a structure that detects a voltage of each unit cell, JP 2012-138284 A (PTL 1) describes using a flat cable as an electric wire for voltage detection, arranging this flat cable along the stacking direction of the unit cells that are stacked in parallel, and connecting this flat cable and the electrodes of the unit cells by conductors such as busbars. The flat cable has a plurality of rows of core wires arranged in the width direction, and the core wires of the flat cable and the conductors such as the busbars are connected by clip-shaped terminals.